This invention pertains to a tilt switch apparatus and method, especially for use in bulk material handling such as is required for removal of coal from underground mines.
In the mining arts, it is well known that a tip or tilt switch may be utilized to detect any of a variety of conditions such as a skewed conveyor belt, an over-filled hopper, or a plugged feed chute.
Typically, the known tilt switch apparatus for such purposes may comprise a switch housing that hangs vertically from a flexible support such as a chain within the confines of a power fed coal bin, for example. An electrical cable, which is separate from the switch hanger, connects a single tilt switch element such as a mercury switch within the switch housing to a control circuit for control of the feeder that delivers coal to the bin. If the feeder delivers the coal at a greater rate than it is being removed from the bin, the coal level in the bin will rise until the switch is tilted sufficiently from vertical to actuate the switch element contacts and turn off the feeder, thus preventing an over-fill condition in the bin.
Typical examples of such prior switches are the products of Ramsey Engineering Company and American Mine Research, Inc., and specifically Tip Switch Model TS1900 of the latter. Other prior art motion or position sensitive switches known to applicant include those discussed in U.S. Pat. Nos. 3,657,695, 3,362,023, 4,163,127, 3,030,477, 4,156,236, and 4,450,325.
The prior tip switches known to the applicant herein have incorporated only a single, normally closed switch element such as a mercury switch, and have been provided with separate switch hanger and electrical power feed arrangements. Often there have been problems with interference between the switch hanger structure and the electrical cable, as well as with extreme and rapid wear and premature failure of the electrical cable, especially in underground mining environments. Thus it may be seen that the prior art tip switches have been subject to various undesirable limitations regarding electrical cable durability, hanger integrity, and reliability of operation.
Another shortcoming of the prior art is that tip switches commonly have been utilized in mines only to exert control upstream from the problem area. For example, conventionally when a tip switch responds to an over-fill condition in a bin, it operates to discontinue the feed of material to the bin. Although this response may be effective to prevent further aggravation of the over-fill condition, it does not alleviate the condition. Thus, the conventional tip switch function has been of limited value. The use of tip switches exclusively for this sort of control function in the prior art is related to the relative desirability of normally closed versus normally open switch contacts. In some applications, using a switch with normally closed contacts is not desirable where the control circuitry is not designed to accept this type of input. The alternative is a tip switch provided with a special, normally open switch element that closes upon actuation to complete a circuit.
Although such switch elements are known, they have not been practical for application in a tilt switch that must actuate upon tilting to a specified angle in any direction.